1. Technical Field of the Invention
The present invention generally relates to dynamically switched optical transport networks. More particularly, and not by way of any limitation, the present invention is directed to a constraint-based shortest path first method for such networks.
2. Description of Related Art
Of the functions performed by a transport network, traffic routing (i.e., the steering of traffic through the transport network in the most effective way) and service provisioning are of primary importance. Historically, these functions have been performed manually. In the near future, it is likely that these functions will be performed using a combination of the latest technologies, including Traffic Engineering (“TE”) and Generalized Multi-Protocol Label Switch (“GMPLS”) technologies. TE supports the network-wide performance optimization. GMPLS supports the switching of network services based on Internet-based algorithms.
Typically, upon receiving a network traffic demand, a signaling entity in an ingress transport network element (“TNE”) signals the creation of a Label Switched Path (“LSP”) on a predetermined strict explicit route using a network resource reservation protocol, such as RSVP-TE or LDP. To determine a strict explicit route for each traffic flow, a path selection algorithm that can be initiated in an on-demand basis must be implemented in each TNE in the GMPLS transport domain. The determined strict explicit route must fulfill traffic demands, including level of service and diversity requirements, and route specifications, including the ingress and egress TNE addresses. The transport network resource availability and its topological information are critical for successful setup of the corresponding LSP and are maintained and frequently updated in the TE network database (“TEND”) by a TE Internet Gateway Protocol (“TE-IGP”), such as OSPF-TE or ISIS-TE. As the determination of a strict explicit route is in-line in the path establishment timeline, the performance of the path selection method is of primary importance to minimize setup delays.
Constraint-based routing (“CBR”) in the GMPLS control plane domain is one of the main processes required for on-demand service provisioning, or “bandwidth-on-demand”, and for dynamic service restoration, which are considered two of the main incentives for the use of GMPLS in optical transport networks (“OTNs”). CBR is defined as the mechanism for computing a feasible network path from a source, or ingress, TNE traffic bearing port to a destination, or egress, TNE traffic bearing port on a network demand, which includes a set of traffic description parameters and a set of service constraint parameters for the desired connection path. The key technical issues with respect to CBR are determining a set of constraint parameters to be taken into account during path calculation, developing a path selection algorithm for calculating the most competitive path from an ingress TNE to an egress TNE within the OTN domain, and performing the path calculation in the shortest amount of time possible to minimize connection cut-through time.
For many service providers, providing multiple levels of service to meet different customer requirements is vital for the success of their businesses. The ability to provide resource assurance and service differentiation in a network, whether public or private, is often referred to as “Quality of Service” (“QoS”). Implementation of some form of CBR in GMPLS domains to support QoS functionality is a prominent issue both in research and development areas of telecommunications.
Various solutions may exist for implementing limited forms of CBR in a GMPLS domain, depending on the constraints and type of transport network under consideration; however, there is no known solution supports the level of flexibility that will be desirable in connection with current and future transport networks.